Did Huge Volcanic Blasts Snuff Out Dinos?
for National Geographic News
|August 23, 2005|
A buildup of gases caused by huge volcanic eruptions may have killed off the dinosaurs, according to new research from one the largest lava flows in Earth's history.
Known as the Deccan Traps, the massive lava deposits in west-central India are over a mile (two kilometers) thick and span an area comparable to Oregon and Washington State combined.
The geologic formation appeared 65 million years agoaround the time of the Cretaceous-Tertiary mass extinction that wiped out some 85 percent of Earth's species.
A team of French and Indian geologists recently reported that the Deccan Traps lava might have piled up so quickly that climate-altering sulfuric gases from the eruptions could have made Earth's environment deadly to many species.
New tests reveal that one 2,000 foot-thick (600 meter-thick) lava section could have accumulated in just 30,000 years. That's lightning-fast by geologic standards.
"Our working hypothesis is that the majority of the total volume of lava might have been erupted in only a few major events spread over only a small fraction of millennia," said Anne-Lise Chenet of the Paris Geophysical Institute's paleomagnetism laboratory.
"Volcanic eruptions can inject large amounts of sulfur dioxide into the atmosphere. If [little] time passes between different volcanic processes, you change the climate and have a big impact on the environment," she said.
"That's why we began the study, because we wanted to know how many different volcanic processes [were] necessary to produce the volume of lava [at Deccan Traps]."
The geologic formation is a vast deposit of basaltic lava, which sprawls nearly 200,000 square miles (500,000 square kilometers). The Deccan Traps are believed to have formed during volcanic activity that spanned about a million years.
But the new dating results suggest that large portions of lava may have come in spurts much closer together than previously thought.
Chenet described her team's research at a joint meeting of the Geological Society of America and the Geological Association of Canada in Calgary earlier this month.
"Smoking Gun" Is Elusive
Scientists have found strong links between other mass extinctions and volcanic activity.
"At least two other great extinctions may have had massive volcanic activity as a prime cause: the greatest of all extinctions, at the Permian-Triassic boundary 251 million years ago, and the mass extinction at the Triassic-Jurassic boundary 200 million years ago," said Hans-Dieter Sues, associate director for research and collections at the Smithsonian Institution's National Museum of Natural History.
"In each of these cases, there are vast areas of volcanic activity far exceeding the Deccan Traps in area and volume." Scientists say the Deccan Traps undoubtedly had a significant impact on the planet, but the volcanic event's precise role in the Cretacious-Tertiary's great extinction remains unknown.
"It would be inconceivable that you could have an eruption on this scale without having some sort of global climate effect," said Thomas Holtz, a vertebrate paleontologist at the University of Maryland in College Park.
"Certainly it would have made life difficult for organisms all over the world," he added. "But it is yet to be shown that there was an extinction associated with these eruptions."
Holtz suggests that dinosaurs may have been stressed by the effects of the Deccan Traps eruptions. But they survived until the arrival of a city-sized asteroid that plowed into Mexico's Yucatán Peninsula 65 million years ago.
The so-named Chicxulub impact clouded the planet's atmosphere with enormous volumes of ash and debris and is commonly thought to be a cause of the Cretaceous-Tertiary extinction.
"We have evidence of all sorts of animals, in the sea and on land, occurring right up to the [Cretaceous-Tertiary] boundary. Those species were surviving whatever effects the Deccan Traps produced," Holz said.
Both Hotlz and Sues, of the Smithsonian, suggest that a number of events, including the massive lava flows and the subsequent catastrophic asteroid impact, as well as mountain building and changing global sea levels, might have worked combination to snuff out the dinosaurs.
"Maybe a massive extinction can't have a single cause," Holtz speculated. "Maybe they are always one-two punches, where something happens to cause environmental stress, species cope to some degree; and then something else comes along that is additionally catastrophic, so that [species] can't recover."
Chenet, of the Paris Geophysical Institute, agrees that India's ancient volcanic eruptions and the Chicxulub asteroid impact produced a deadly combination. But she suggests that the lava flows might well have finished the job on their own.
"Our view is that [asteroid] impact added to the stress already generated by an ongoing massive eruption, enhancing significantly the extent of the extinction, which would, however, have taken place even if the impact had not occurred."
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